Cathode for electrical discharge devices



Feb. 13, 1934. c, J. R. H. voN wl-:DEL ,1,945,603

Y CATHODE FOR ELECTRICAL DISCHARGE DEVICES "gmx Filed May 9, 1929Patented Feb.` 13, 1934 UNITED STATES PATENT i OFFICE CATHODE FORELECTRICAL DISCHARGE DEVICES Carl J. `R. H. von Wedel, Berlin, Germany,as-

signor to Electrons, Inc., a` corporation of Delaware Application May 9,1929. Serial No. 361,652 19 Claims. (Cl. Z50-27.5)

substance is used, and moreliparticularly to fla- Figure 1 is aperspective view of a segment of mentary or directly heated cathjdes forelectric my improved CathOde,

5 discharge tubes. The features of the invention Figures 2, 3 and 4illustrate the manner in 60 oiier particular advantages connection withWhich the 0016 0f my impIOVed CahOde iS Conlarge current and highpotential discharge de- Structed, and vices, as in heavy duty rectifiertubes, but may Figure 5 illustrates the action of my improved be appliedwith advantage to tubesehaving those cathode flo-operating with an anodein a recti- 10 characteristics usual for radio receiving and like fiertube. 65 amplifying systems. Referring to Figure 1, the cathodecomprises since the beneficial results of my invention are a core 1having a helical rib 2 between the spaced better emphasized inConnection with a, heavy turns of which is embedded a filling 3 of anelecduty gas-filled rectiiier tube I hereinafter detrOn @missive'COmDound preferably 011e 0f the Heretofore in the prolonged use ofdischarge the favorable influence of the core materials on 75 Inaddition to the causes pointed out in said mi Zirc0nium`Barium zirconate; 85 patent for the waning of space current with use 9T Wlththese c ompounds smgly or as mlXPues I have found that when operatingwith high cur interchanged wlthlthe metals or those emlsslve rents andhigh potentials the emissive coatings ggugsag;glllzlfthtebrlllyalmlarsngtlrsl rg; undergo severe physlcal disturbanceseven to the those emissive double metal compounds in which 90 emissivecoating from its support; and also that talle elerfent oxx'genpas benreplaced .by sul arcing effects may occur and be most destructive p mi mregen uorme Car on or arsemo' to the coating and its support.

It is the object of the present invention to materially eliminate anyloosening of the coating 4 pounds less acid than titanic acid, andanother 100 quick destruction of the cathode due to increased core 4 ofsumcient Size to carry the heating cur 105 come electromcally inert sothat further destrucwith a surface 5 of another metal such as nickeltion at the point will not occur. by any of the usual electro-plating orother Further objects w1l1 appear as the description processes. Uponthis coated core, I wind a helix 110 having preferably a pitch equal toone and onehalf times the diameter of the wire 6 of the same or asimilar metal, the resultant product being shown in Figure 3. I thentreat the structure of 5 Figure 3 in an electrolytic or other bathcontaining one of the above mentioned metals, such as nickel, so thatthere is produced a. coating or plating over the entire structure, withthe result that the turns of the helix 6 are metallically and iconductively connected to the surface 5 as shown at 'l in Figure 4. (SeeFigs. 1 and 5.) In this manner I have produced a helical dove-ta grooveabout the core in which I place the filling of emissive compound 3, forexample, barium l aluminate, filling the dove-tail groove substantiallyto the outer diameter of the helix 6.

When this type of cathode is used with a closely associated anode 8having high potential, the emissive coating being securely held withinthe "dove-tail groove of the cathode, there is little possibility of thecoating being loosened and torn from the core.

This type of cathode has particular advantages in gas lled rectifiertubes. The electron cloud around the cathode neutralizes the ions of thedischarge to prevent ionic bombardment, and the neutralizing is mosteffective because such a cathode arrangement has a very large effectiveemitting surface, enhanced by the fact that the emissive coatingcontinuously creeps over the surface of the helix 6 maintaining anundulated eiective emissive surface.

Further, should an arc occur between the anode and the cathode, Fig. 5,such arcing will 85 occur between the helix 6 and the anode 8 with theresult for instance that, a portion of the helix 6 will be burned awayas illustrated at 9. Even though the cross-section of the cathode properat this point is reduced by this action, it is still greater than thecross-section of the core proper at a point between the turns of thehelix 6, so that no hot-spot is produced on the cathode by reason ofreduction of current carrying cross-sectional area. The creepingcharacteristic of the emissive coating during operation soon covers overthe injured spot so that the original characteristic emission from thisportion ensues. Should the arcing continue for a sufficient length oftime that a portion of the cathode is pitted as shown at 10 sufcientlydeep to penetrate to the core 4, the ionic bombardment of the gas uponthe exposed core metal, together with the creeping of the emissivecoating thereover, will form a non-emitting coating at 11 for 5i thereasons set forth in the aforementioned patent, so that at thetemperature at which such a cathode is designed to operate, usuallyabout 800 C., emission at this point stops even though this point isrelatively hotter than the rest of the cathode. In this manner thedestruction of the cathode at this point is stopped. Since in generalthese spots, ii occurring, are of small area d t the rest oi the cathodethe reas compare 0 maining emissive surface will easily pfovle necessaryemission iordco'isneugsgacem. thihlitl): Iviltigvteusibecherein aSpecific @pist-1 sive cathode structure in which I have mme the metals dprefer to tungsten and nickel, an

bstances cereon as electron emissive su tlntilnpounds such as compoundsof the high 1y electropositive metals in the form of zincatels, materia.s

s .and zirconiates or other s:iiflz'laima;@the iiuorides of these metalsand those previously mentioned, and specically barium aluminate, it isto be understood that other metals and other emissive compounds, such asthose proposed by Wehnelt, or barium oxide, strontium oxide and calciumoxide, or mixtures thereof, may be used without departing from thespirit of my invention as defined in the claims appended hereto. f

Having thus described my invention what I claim is:

1. In a cathode structure, the combination of a cylindrical core, ahelix of wire wound upon said core, a metallic junction between the wireand said core whereby said wire is incorporated integrally upon saidcore, and an electron emissive substance between the turns of saidhelix.

2. In a cathode structure, the combination of a core of highlyrefractory metal, a coating of a metal upon said core, capable bychemical conversion of forming an amphoteric compound less acid thantitanic acid, a helical rib of said metal integral with said coating andsurrounding said core, and an electron emissive material between thetunis of said helical rib.

3. In a cathode structure, the combination of a core of highlyrefractory metal, a coating of nickel upon said core, and a helical ribof nickel metallically joined to said coating.

4. In a cathode structure, the combination of a core of highlyrefractory metal, a coating of nickel upon said core, and a nickel wirehelically wound over said coating and metallically integral therewith,said nickel wire forming a helical dove-tail groove around said core.

5. In a cathode structure, the combination of a core of tungsten, aplating of nickel upon said core, a nickel wire helically wound uponsaid core and metallically joined to said plating, and an electronemissive compound between the turns of said helix.

`6. In a cathode structure, the combination of a core of highlyrefractory metal, a nickel Wire helically woundupon said core andmetallically integral therewith, an electron emissive material includingbarium nickelate between the turns of said helix.

7. The process of production of a cathode structure which comprisesplating a core of tungsten with metallic nickel, Winding a helix ofnickel wire upon said plating, immersing said core and said helix in abath containing nickel, by electrolysis metallically joining said helixto said plating and filling in the space between the turns or said helixwith an electron emissive material which reacts with said nickel to formbarium nickelate.

8. In a cathode structure, the combination of a refractory metal core, acoating of metal upon said core which by chemical conversion forms anamphoteric compound less acid than titanic acid, and a helical rib of asimilar metal upon said 135 coating and metallically joined thereto.

9. In a cathode structure, the combination of a core of refractorymetal,i a coat'iig o said core capable of orming y 0 e me@ a maartrattasse 14 eica ri a. or highly electroposltwemetal ailleenetal combychemical -conversion atalcfhe Said Compound pound with said coating meid helix. beg pohloewstirutlr griabination of 1 a f metal 0 metal, a'Plat-'mg o cifedrnetai being capable by Clgg 5o ical conversion offorming an amphftenc 1 pound less acid than titanic acid, a helical Wireof said metal wound upon said plating and electrically joined thereto,and an electron emissive compound containing a metal capable of formingby chemical conversion an amphoteric compound less acid than titanicacid, said emissive compound being disposed between the turns of saidhelix.

ll. In a cathode structure, the combination of a core containing, atleaston itssurface, a metal capable of forming by chemicalf. .cnversionan amphoteric compound less acid than titanic acid, a helical wire ofsaid metal wound upon said core and electrolytically joined theretoforming a helical dove-tail groove around said core, and an electronemissive compound, capable of forming a double-metal compound with saidmetal on the core surface, disposed within said dove-tail groove.

12. The method for making a cathode structure which comprises coating ametal core with another metal, winding a helix of wire over saidcoating, electrically joining said helix to said metal coating, andapplying a thin coating of electron emissive material to lthe outerportions of the helix and athick coating thereof to the corey coatingand helix between turns of the latter.

13. 'I'he method for making a cathode structure which comprises platinga refractory core with a metal, winding a helix of wire upon saidplating, and electrically joining said helix to said plating with anadditional plating of said metal on both core and helix.

14. In a lamentary cathode structure, the combination of a metalliccore, a series of metal ribs upon said core, a metallic junction betweenthe ribs and the core whereby said ribs are incorporated integrally uponthe core, and an electron emissive substance between said ribs.

15. In a cathode structure, the combination oi' a refractory core, acoating of nickel on said core, a metal wire helically wound on the saidcore, means for maintaining a metal to metal contact between each turnof the wound wire and said coating, and a substance of electron emittingcapacity applied to the said wire.

16. In a cathode structure, the combination of a core at least the outersurface of which is nickel, a metal Wire helically wound on said corewith each turn of the wire forming with the nickel surface a permanentmetallic contact having a lo'wer electrical resistance than a turn ofthe wound wire, and a substance of electron emitting capacity applied tothe said wire.

17. In a cathode structure, the combination of i a core of a metalcapable of forming by chemical conversion an amphoterio compound lessacid than titanic acid, a wire of a similar metal helically wound on thesaid core and metallically joined thereto for at least a portion of eachturn of the Wound wire, and a substance of electron emitting capacityapplied to the wire.

18. In a cathode structure, the combination of a lamentary core having asurface of nickel, a series of nickel ribs upon said surface andmetalically joined thereto, and an electron emissive substance betweensaid ribs.

19. In a cathode structure the combination of a core having a metallayer for its outer portion, said metal being capable of forming bychemical conversion an amphoteric compound less acid than titane acid, ametal wire helically wound on said metal layer, means for metallicallyconnecting the turns of said wire to the surface of said metal layer,and a substance of electron emitting capacity applied to said wire.

CARL J. R. H. VON WEDEL.

